For more than half a century, the cathode ray tube (CRT) has been the principal electronic device for displaying visual information. The widespread usage of the CRT may be ascribed to the remarkable quality of its display characteristics in the realms of color, brightness, contrast and resolution. One major feature of the CRT permitting these qualities to be realized is the use of a luminescent phosphor coating on a transparent faceplate.
Conventional CRT's, however, have the disadvantage that they require significant physical depth, i.e., space behind the actual display surface, making them bulky and cumbersome. They are fragile and, due in part to their large vacuum volume, can be dangerous if broken. Furthermore, these devices consume significant amounts of power.
The advent of portable computers and other miniaturized devices has created intense demand for displays which are light-weight, compact and power efficient. The space available for the display function of these devices precludes the use of a conventional CRT. Accordingly, significant efforts have been made to provide satisfactory flat panel displays having display characteristics, e.g., brightness, resolution, versatility in display and power consumption which are comparable or superior to those of CRT's. These efforts, while producing flat panel displays that are acceptable for some applications, have not produced a display that can compare to a conventional CRT.
Currently, liquid crystal displays are used almost universally for laptop and notebook computers. In comparison to a CRT, these displays provide poor contrast, permit only a limited range of viewing angles, and, in color versions, consume power at rates which are incompatible with extended battery operation. In addition, color liquid crystal screens tend to be far more costly than CRT's of equal screen size.
As a result of the drawbacks of liquid crystal display technology, thin film field emission display technology has been receiving increasing attention from industry. Flat panel displays utilizing such technology employ a matrix-addressable array of pointed, thin-film, cold field emission cathodes in combination with an anode comprising a phosphor-luminescent screen.
The phenomenon of field emission was discovered in the 1950's, and extensive research by many individuals has improved the technology to the extent that its prospects for use in the manufacture of inexpensive, low-power, high-resolution, high-contrast, full-color flat displays appear to be promising.
Advances in field emission display (FED) technology are disclosed in U.S. Pat. No. 3,755,704, "Field Emission Cathode Structures and Devices Utilizing Such Structures," issued 28 Aug. 1973, to C. A. Spindt et al.; U.S. Pat. No. 4,940,916, "Electron Source with Micropoint Emissive Cathodes and Display Means by Cathodoluminescence Excited by Field Emission Using Said Source," issued 10 Jul. 1990 to Michel Borel et al.; U.S. Pat. No. 5,194,780, "Electron Source with Microtip Emissive Cathodes," issued 16 Mar. 1993 to Robert Meyer; and U.S. Pat. No. 5,225,820, "Microtip Trichromatic Fluorescent Screen," issued 6 Jul. 1993, to Jean-Frederic Clerc. These patents are incorporated by reference into the present application.
The Clerc ('820) patent discloses a field emission flat panel display having a glass substrate on which are deposited a matrix of conductors. In one direction of the matrix, conductive columns comprising the cathode electrode support multiple microtips. In the other direction, above the column conductors, are perforated conductive rows comprising the gate electrode. The row and column conductors are separated by an insulating layer having holes permitting the passage therethrough the microtips, each intersection of a row and column corresponding to a pixel.
One area for improvement of field emission displays of the current technology is in increasing the display size. The largest display size realized by today's technology is approximately 8".times.6" (10" diagonal). What is needed is an ability to manufacture larger size displays for use in systems such as engineering work stations. More ideally, what is needed is a large FED display where one high resolution image can be viewed and updated independently of at least one other image.